The invention relates to an electrochemical energy storage apparatus, in particular a rechargeable lithium-ion battery having at least one current collector device. An energy storage apparatus of this type is known from EP 2 595 219 A1.
The invention is described below with reference to an electrochemical energy store for a motor vehicle for supplying the driving motor with electrical power (traction battery); this should not be understood as a limitation of the invention to such an application.
Rechargeable batteries having highly reactive contents are generally used in motor vehicles. Therefore, the safeguarding of said rechargeable batteries is of great importance. Due to external loads, the storage battery may become deformed in the event of an accident. It is generally considered advantageous if the rechargeable battery withstands a high degree of deformation without reacting in an uncontrolled manner.
One reason for an uncontrollable reaction of the rechargeable battery can arise due to a short circuit of the anodes with the cathodes; in this case, the contents of the rechargeable battery can ignite due to heating or sparking and can react further. A short circuit of this type can be caused by the penetration of electric conductors, such as the latter in the form of what are referred to as current collectors, within the rechargeable battery. The current collectors or current output conductors are intended firstly to be able to be produced cost-effectively, but also, during regular operation, to have the function of diverting current from the anodes/cathodes (electrodes) to the electric terminal of the rechargeable battery. This in particular permits electrical contact connection of the energy storage cell to the outside. In the event of a crash, they are not intended, or are intended only to a small extent, to lead to a short circuit in the rechargeable battery or in an energy storage cell.
Current output conductor devices having two symmetrically formed current conductor arms are known from EP 2 595 219 A1, wherein the current conductor arms are oriented parallel to separator contact areas, i.e. to separating areas between the electrodes.
It is an object of the invention to increase the operational reliability of an electrochemical energy storage apparatus; in particular, it is a further object of the invention to increase the storage density of the rechargeable battery.
This and other objects are achieved by an electrochemical energy storage apparatus, in particular a rechargeable lithium-ion battery, having at least one current collector device with at least one current conductor arm, and at least one energy storage cell which has at least one anode, one cathode and one separator. The separator touches the anode and the cathode at least in sections in, in each case, a separator contact area. The current conductor arm can be electrically conductively connected to, in each case, at least one anode or cathode by way of a current output conductor contact area. A surface normal on the current output conductor contact area and a surface normal on the separator contact area form an acute angle α. This angle α is selected from a range which is greater than 5°, with preference greater than 15°, preferably greater than 25° and particularly preferably greater than 35°, and furthermore the angle α is less than or equal to 90°, with preference less than 75°, preferably less than 65° and particularly preferably less than 45°.
At least one or more electrochemical energy storage cells are arranged in an electrochemical energy storage apparatus. In an electrochemical energy storage cell of this type, anodes and cathodes are layered, wound or stacked and are, in each case, separated from one another by a separator. Such a stack of cells or windings can be understood in particular to be the electrochemically active part of the energy storage cell. The anodes and/or the cathodes are preferably electrically conductively contacted at least in sections by a current collector device. The current collector device preferably has one or more current conductor arms. The current conductor arms contact the anodes and/or the cathodes within a current output conductor contact area. The contact areas between the separator and the anodes and/or cathodes and the current output conductor contact area are generally oriented parallel to one another in the known prior art. An energy storage cell preferably has a length, width and a thickness. The thickness of the storage cell is substantially determined here by the number of layers (anode, cathode, separator). It is known from the prior art that the current output conductor contact area extends, at least in sections, in the length and width direction.
According to the invention, a surface normal on the current output conductor contact area, or preferably on a tangential plane on said contact area, and a surface normal on the separator contact area encloses an acute angle α. Furthermore preferably, the acute angle α is selected from a range which is >5°, with preference >15°, preferably >25° and particularly preferably >35°. Furthermore, the angle α is ≤90°, with preference ≤75°, preferably <65° and particularly preferably <45°.
Within the context of the invention, an electrochemical energy storage cell should be understood as meaning a device in which electrical energy can be stored in chemically bound form and which has at least two, but preferably a multiplicity of, layers for said storage. An electrochemical energy storage cell preferably has at least one anode and one cathode, wherein said anode and cathode are with preference layered or preferably stacked; constructional forms of this type are known in the case of lithium-ion storage cells as so-called jelly-roll cells, pouch cells or coffee bag cells. Furthermore preferably, a storage cell of this type should be understood as meaning a lithium-ion energy storage cell or lithium-air energy storage cell. Furthermore preferably, a cell of this type at least substantially has a prismatic basic geometry, in particular in contrast to cylindrical or rod-shaped storage cells.
Furthermore preferably, the storage cell is designed as a so-called coffee bag cell, pouch cell or jelly roll cell. Cells of this type share the feature in particular that they have a longitudinal extent, a width extent and a thickness extent, wherein the thickness extent is smaller, in particular substantially smaller (at max. 50%), at least one of the two other extents. The thickness extent is substantially determined here by the number of layered anodes, cathodes and separators, whereas the width and longitudinal extent can be more or less freely determined.
Within the context of the invention, a current collector device should be understood as meaning a device for the electrically conductive connection of the electrochemically active part of the energy storage cell to further electric terminals for the electrical contacting of the energy storage cell, in particular to the poles of the energy storage cell. The current collector device is preferably connectable to the electrodes (anodes or cathodes) of the energy storage cell. The current collector device preferably has at least one current conductor arm.
Within the context of the invention, a current conductor arm should be understood to mean a portion of the current collector device that is designed for electrical contacting connection with at least one electrode. Furthermore preferably, the current conductor arm contacts the electrodes in a current output conductor contact area. The current conductor arm preferably extends along or in the direction of a side edge of the energy storage cell, with preference in the direction of the longitudinal extent or preferably in the direction of the width extent. Furthermore preferably, the storage arm is inclined about the extent direction, and in particular, as a result, the current output conductor contact area and the separator contact area are not oriented parallel to each other. In contrast thereto, in the case of current output conductor devices known from the prior art, the current output conductor contact area and the separator contact area are oriented parallel to each other.
Within the context of the invention, a separator contact area should be understood to mean a separating area between two adjacently arranged electrodes (anode/cathode), wherein the latter are separated from each other, at least in sections, by a separator and are contacted by the latter. Furthermore, the separator contact area should be understood as meaning an at least substantially flat contact area between a separator and one of the electrodes. Furthermore preferably, the separator contact area should be understood as meaning an area portion between an electrode and the separator that extends at least substantially in the longitudinal extent and the width extent of the electrochemical energy storage cell. In visual terms, the separator contact area should be understood as meaning in particular a stacking plane of the electrode stack.
In particular by means of an angle α according to the invention between a surface normal on the current output conductor contact area and a surface normal on the separator contact area, a larger current output conductor contact area can be realized within the same construction space. Generally, the electrical resistance of a connection depends in particular on the size of the contact area and tends to drop with a larger area. With an increased current output conductor contact area, it is therefore possible firstly to improve the efficiency of the energy storage apparatus and secondly to increase the operational reliability thereof.
In a preferred embodiment, the current collector device has a second current conductor arm. The second current conductor arm preferably extends in a basically parallel extent to the first current conductor arm. The parallelism preferably does not relate to the inclination of the current conductor arms. Furthermore preferably, the second current conductor arm contacts at least one electrode in a second current output conductor contact area. Furthermore preferably, a surface normal on the separator contact area and a surface normal on the second current output contact area encloses an acute angle β. The acute angle β is preferably selected from a range which is >5°, with preference >15°, preferably >25° and particularly preferably >35°, and furthermore with preference the angle β is ≤90°, with preference <75°, preferably <65° and particularly preferably <45°. In particular, the current output conductor contact area can be further increased by use of two current conductor arms, or electrodes of different potential can be connected to the current conductor arms; in particular, the efficiency and the operational reliability of the energy storage apparatus can thereby be further improved.
In a preferred embodiment, the first and the second current conductor arm are inclined diametrically opposed to each other (angles α, β). In particular because of the diametrically opposed inclination of the current conductor arms, a V-like or roof-like profile is produced in a plane which is arranged orthogonally to the axis of inclination (α, β) of the current conductor arms. Furthermore preferably, the V-like profile is oriented in such a manner that the portion having the smallest distances between the first and the second current conductor arm face the energy storage cell. Investigations have shown that in particular two current conductor arms inclined diametrically opposed to each other have a positive effect on the operational reliability of the energy storage cell.
In a preferred embodiment, the current conductor arms are arranged mirror-symmetrically with respect to each other at least in sections or completely. Preferably, the current conductor arms are arranged mirror-symmetrically with respect to each other in sections or preferably completely, at least in the region of the current output conductor contact areas. In particular by way of this arrangement of the current conductor arms, a particularly simple and cost-effective production of same is permitted.
In a preferred embodiment, the energy storage apparatus has at least one first and one second energy storage cell. Separator contact areas of the first and second energy storage cell are preferably arranged parallel to each other at least in sections. Furthermore preferably, the first current conductor arm can be electrically conductively connected to the first energy storage cell, and the second current conductor arm can preferably be electrically conductively connected to the second energy storage cell. In particular by increasing the number of electrochemical energy storage cells, the storage capacity of an energy storage apparatus can be extended and therefore an improved energy storage apparatus can be produced.
In a preferred embodiment, an imaginary separating area is arranged between the first energy storage cell and the second energy storage cell. The separating area preferably has a flat profile at least in sections or completely. Furthermore preferably, the separating area should be understood as a parallel plane to one or more of the separator contact areas.
The first current conductor arm is preferably arranged in such a manner that at least the current output conductor contact area on the side of the first energy storage cell extends as far as the separating area or is spaced apart therefrom in sections or completely by a distance t1. Furthermore preferably, the second current conductor arm is arranged in such a manner that the latter or the second current output conductor contact area, on the side of the second energy storage cell extends as far as the separating area or is spaced apart therefrom in sections or completely preferably by a distance t.2. In particular, in the event of an unplanned deformation of the electrochemical energy storage apparatus (crash situation), it has proven particularly advantageous if the current conductor arms are arranged as described, in particular with an inclination.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.